One form of testing in oil and gas wells can be performed by shut-in measurements. In such tests, an interval of the well is isolated by means of a packer or the like. Fluids are allowed to flow from the formation in the interval and through a conduit to the surface. By closing a valve in the conduit (shut-in), flow is stopped and the pressure of the fluid in the interval builds up until the pressure in the interval balances the pressure in the fluids in the formation, and flow stops. By monitoring the build-up of pressure in the interval after shut-in, properties of the well and formation can be determined.
The speed at which the valve is closed, and the position of the valve in the conduit will have an impact on the pressure build-up after shut-in. In one form of test, known as a drill stem test (DST), the conduit extends from the isolated interval to the surface of the well, where the valve is located. Consequently, the volume of the interval and conduit (drill stem) can be high, leading to a significant storage effect that can have a substantial effect on the pressure build-up after shut-in.
For shut in tools, valve closure times greater than a few seconds can reduce the data fidelity by masking the early time data response and therefore rendering it not possible to discern near wellbore effects and also making it harder to “pick” the initial build up time, which creates an error range on the final buildup analysis.
A number of patents disclose shut-in tools, including: U.S. Pat. No. 5,188,172 which describes a general automatic memory driven shut-in tool; U.S. Pat. No. 6,957,699 describes a fast closing tool which appears to operate using a ball seat valve mechanism; U.S. Pat. No. 7,114,697 which discloses a motor driven actuator trigger and spring driven actuator and well pressure to force the rapid closure; and U.S. Pat. No. 7,823,633 which discloses a system with an inductively coupled link across the valve for data transfer.
This invention aims to provide a valve system that can be configured to operate quickly and that can be implemented in a manner that reduces the effect of the volume of the interval and conduit.